Optical fibers have been put into practice in various fields because of such advantageous properties as to transmit signals at a lower loss, not to be electrically interfered with and to be formed at a lighter weight and with a small diameter.
Oceanic development has actively been promoted in recent years in exploring natural resources, fishery, construction of submarine cables and pipe lines or in maintenance thereof. Optical fibers have proved to be applicable in such fields. An example of such application is the use of optical fibers as a signal line in a composite control cable connecting a mother ship to a submersible, taking advantage of the composite control cable's power transmission function, signal transmission function and high tensile strength. The composite control cables are naturally required to be light in weight and small in diameter and moreover, transmitted signals should be free from interference from power lines. Optical fibers satisfy such requirements.
When optical fibers are used underwater, the connector connecting the optical fibers to submerged machines or tools is required to have a water-tight construction. In the prior art, ordinary connectors for optical fibers for use on land were covered entirely with a water-tight, pressure-resistant shell and used as water-tight optical fiber connectors underwater but difficulties arose in handling as the size of the connectors grew larger.